The present invention relates to power transmissions and, more particularly, to a family of power transmissions having three planetary gearsets that are controlled by five torque-transmitting devices to provide at least six forward speed ratios and one reverse ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978, U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000, U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992, and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three and four speed automatic transmissions and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches and three brakes. The Koivunen and Beim patents utilizes six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and another reverse ratio. The Lepelletier employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining two planetary gear sets.
It is an object of the present invention to provide an improved family of transmissions having three planetary gearsets controlled to provide at least six forward speed ratios.
In one aspect of the present invention, the family of transmissions has three planetary gearsets each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear or a planet carrier assembly member. In another aspect of the present invention, each of the planetary gearsets may be of the single pinion type or of the double pinion type. In yet another aspect of the present invention, the first member of the first planetary gearset and the first member of the second planetary gearset are continuously interconnected by a fixed interconnection member.
In still another aspect of the present invention, a second interconnecting member continuously interconnects a second member of the second planetary gearset with a first member of the third planetary gearset. In yet still another aspect of the present invention, a second member of the first planetary gearset is continuously connected with a stationary transmission member, such as a housing or transmission case. In a yet a further aspect of the present invention, each family member incorporates an input shaft which is continuously connected with a member of one of the planetary gearsets and an output shaft which is continuously connected with another member of one of the planetary gearsets.
In a still further aspect of the present invention, the five torque-transmitting mechanisms comprise four rotating type torque-transmitting mechanisms and one stationary type torque-transmitting mechanism. In still a further aspect of the present invention, the stationary torque-transmitting mechanism selectively connects a member of the first, second or third planetary gearset with a stationary member of the transmission, such as a transmission housing. In yet still a further aspect of the present invention, a first of the rotating torque-transmitting mechanisms selectively connects a member of the first planetary gearset with either the input shaft, the output shaft, or a member of the second or third planetary gearset.
In another aspect of the present invention, a second of the rotating torque-transmitting mechanisms selectively interconnects a member of the second planetary gearset with either the input shaft, the output shaft, one of the fixed interconnecting members, or a member of the first or third planetary gearset. In a yet still further aspect of the present invention, a third of the rotating torque-transmitting mechanisms selectively connects a member of either the first, second or third planetary gearset with either the input shaft, the output shaft, or another member of the first, second or third planetary gearset. In yet still a further aspect of the present invention, a fourth of the rotating torque-transmitting mechanisms selectively interconnects a member of the first, second or third planetary gearset with either one of the fixed connecting members or another member of the first, second or third planetary gearset.
In still another aspect of the present invention, the five torque-transmitting mechanisms are selectively engageable in combinations of two to yield at least six forward speed ratios and one reverse ratio. In yet another aspect of the present invention, at least one family member is controlled by the torque-transmitting mechanism to establish eight forward speed ratios, and at least three of the family members are controlled by the torque-transmitting mechanisms to provide at least seven forward speed ratios.